1. Field of the Invention
The present invention relates to apparatus for inspecting the interior of piping. In particular the present invention relates to piping inspection, instrumentation-carrying apparatus having the capability of locating and scanning a specific feature along the interior of the piping.
2. Discussion of Background
Throughout industry, piping is used to convey fluids of every kind over short distances and long. Because of the adverse effects of stress, temperature, and fluids flowing through pipes, both the effects of specific fluids (corrosion) and the effects of fluid flow in pipes generally (erosion), the piping will eventually degrade and may fail completely or may cease to be serviceable or may simply begin to leak. Flaws frequently begin to form at welded joints. However, even newly welded pipe joints can also have flaws that will cause leaks or pipe failure.
The integrity of piping is an important industrial concern and can become crucial depending on a number of factors, including the volume of material transported by the piping per day, the hazardous nature of the material, the cost of the fluid transported, and the impact of a loss of the fluid on the user's operation at the fluid's destination.
Pipe inspection can prove very useful in avoiding pipe failure by determining the condition of piping and how that condition changes over time. Welds can be inspected visually, ultrasonically and using eddy currents. Not only is periodic pipe inspection useful during operation, but pipe inspection prior to use may be especially important. For example, it is prudent to conduct a pre-service inspection of piping that will carry hazardous or radioactive fluids to verify the condition of welds or to fix flaws before the interior of the piping becomes contaminated.
There are a number of piping inspection devices. Some of these are self-propelled and others are pulled or pushed by pipe crawlers or other means. See for example the pipe inspection devices described by Wentzell in U.S. Pat. No. 4,581,938, Takagi, et al. in U.S. Pat. No. 4,621,532 and Weber, et al. in U.S. Pat. No. 4,460,920. Pipe inspection can be done by ultrasonic transducers, eddy current sensors and visual devices. See Metala, et al. (U.S. Pat. No. 4,856,337), Krieg, et al. (U.S. Pat. No. 4,769,598) and Weber, et al. Weber includes a television camera with his pipe inspection device. Metala, et al. and Krieg, et al. carry both ultrasonic and eddy current measuring equipment. A companion application, commonly assigned, titled "Pipe Crawler With Extendable Legs", Ser. No. 679,497 filed Apr. 2, 1991, now U.S. Pat. No. 5,121,694 is incorporated by reference and describes a system for distribution of air via manifolds and solenoid switches. Also, see issued U.S. Pat. No. 5,018,451, commonly assigned, for a description of another pipe crawler such as could be used to move a pipe inspection apparatus.
Inspecting the interior of piping must be coupled with a fairly accurate system for knowing where the inspection device is and how it is oriented. Sometimes only distance in one direction is needed, distance that can be obtained from a simple odometer or from the length of the tether, for carrying power cables, air hoses, and the like, that trails from the inspection device to the entrance of the pipe. If the pipe has a number of bends and variations in diameter, and especially if the area to be inspected is relatively small, more precise locational information may be needed, sometimes, in fact, full coordinate information. The device as described by Thome in U.S. Pat. No. 4,506,549 provides position information in four dimensions: axial, radial, azimuthal and rotational about itself.
However, there remains a need for a pipe inspection device that is capable of making minute inspections and of knowing the precise location of the inspected areas for comparison to previously inspected areas. Fine inspections can enable pipe flaws and changes in those flaws to be detected, analyzed and corrected sooner rather than later.